1. Field of the Invention
The present invention relates generally to subterranean pipe string joint locators, and more particularly, to a joint locator for positioning on a well tool connected to coiled tubing in a well and which has a pressure differential actuated piston controlled by a pilot solenoid valve.
2. Description of the Prior Art
In the drilling and completion of oil and gas wells, a wellbore is drilled into the subterranean producing formation or zone of interest. A string of pipe, e.g., casing, is typically then cemented in the wellbore, and a string of additional pipe, known as production tubing, for conducting produced fluids out of the wellbore is disposed within the cemented string of pipe. The subterranean strings of pipe are each comprised of a plurality of pipe sections which are threadedly joined together. The pipe joints, also often referred to as collars, are of an increased mass as compared to other portions of the pipe sections.
It is often necessary to precisely locate one or more of the pipe joints of the casing, a liner or the production tubing in the well. This need arises, for example, when it is necessary to precisely locate a well tool, such as a packer, within one of the pipe strings in the wellbore. The well tool is typically lowered into the pipe string on a length of coiled tubing, and the depth of a particular pipe joint adjacent to or near the location to which the tool is positioned can be readily found on a previously recorded casing joint or collar log for the well. That is, after open hole logs have been run in a drilled wellbore and one or more pipe strings have been cemented therein, an additional log is typically run within the pipe strings. The logging tools used include a pipe joint locator whereby the depths of each of the pipe joints through which the logging tools are passed is recorded. The logging tools generally also include a gamma ray logging device which records the depths and the levels of naturally occurring gamma rays that are emitted from various well formations. The additional log is correlated with the previous open hole logs which result in a very accurate record of the depths of the pipe joints across the subterranean zones of interest referred to as the casing joint or collar log.
Given this readily available pipe joint depth information, it would seem to be a straightforward task to simply lower the well tool connected to a length of coiled tubing into the pipe string while measuring the length of coiled tubing in the pipe string by means of a conventional surface coiled tubing measuring device until the measuring device reading equals the depth of the desired well tool location as indicated on the joint and tally log. However, no matter how accurate the coiled tubing surface measuring device is, true depth measurement is flawed due to effects such as coiled tubing stretch, elongation from thermal effects, sinusoidal and helical buckling, and a variety of often unpredictable deformations in the length of coiled tubing suspended in the wellbore.
Attempts have been made to more accurately control the depth of well tools connected to coiled tubing. For example, a production tubing end locator has been utilized attached at the end of the coiled tubing. The production tubing end locator tool usually consists of collets or heavy bow strings that spring outwardly when the tool is lowered beyond the end of the production tubing string. When the coiled tubing is raised and the tool is pulled back into the production tubing string, a drag force is generated by the collets or bow springs that is registered by a weight indicator at the surface.
The use of such production tubing string end locator tools involve a number of problems. The most common problem is that not all wells include production tubing strings and only have casing or are produced open hole. Thus, in those wells there is no production tubing string on which the tool can catch while moving upwardly. Another problem associated with the lower end of the production tubing string as a locator point is that the tubing end may not be accurately located with respect to the producing zone. Tubing section lengths are tallied as they are run in the well and mathematical or length measurement errors are common. Even when the tubing sections are measured and tallied accurately, the joint and tally log can be inaccurate with respect to where the end of the tubing string is relative to the zone of interest. Yet another problem in the use of production tubing in locator tools is that a different sized tool must be used for different sizes of tubing. Further, in deviated or deep wells, the small weight increase as a result of the drag produced by the end locator tool is not enough to be noticeable at the surface.
While a variety of other types of pipe string joint indicators have been developed including slick line indicators that produce a drag inside the tubing string, wireline indicators that send an electronic signal to the surface by way of electric cable and others, they either cannot be utilized as a component in a coiled tubing well tool system or have disadvantages when so used. One improved coiled tubing joint locator tool and methods of using the tool are disclosed in U.S. Pat. No. 5,626,192, assigned to the assignee of the present invention. This tubing joint locator does not require the use of electric cable and overcomes other shortcomings of earlier prior art. This joint locator has a longitudinal fluid flow passageway therethrough so that fluid can be flowed through the coiled tubing and the joint indicator and has at least one lateral port extending through a side thereof which provides communication between the fluid flow passageway and the well annulus outside the tool. An electronic means detects the increased mass of a pipe joint as the locator is moved through the pipe joint and generates a momentary electric output signal in response thereto. A valve means is actuated in response to the electric output signal to momentarily open or close the lateral port which creates a surface detectable pressure drop or rise in the fluid flowing through the coiled tubing and the joint locator indicative of the location of the pipe joint. The valve is connected to the solenoid and is mechanically directly opened or closed thereby.
In some cases, the output of the solenoid may be insufficient to overcome the friction of the sleeve particularly with smaller tools with size restrictions. The present invention solves this problem by using a pilot operated solenoid valve which communicates fluid pressure to a piston such that the pressure differential inside the tool and outside the tool moves the piston to close a normally open circulating port. The pilot operated solenoid valve decreases the stroke necessary for the solenoid valve and further reduces the power requirements proportionally.
Another potential problem with the apparatus shown in U.S. Pat. No. 5,626,192 is the pressure spike caused by closing the circulation port might interfere with or cause premature operation of pressure sensitive tools which are located in the tubing string below the coiled tubing joint locator. The present invention solves this problem by providing a rupture disk which opens only at a predetermined pressure, and pressure can only be communicated to the rupture disk after circulating a ball through the tubing string and applying sufficient pressure to actuate a sliding sleeve.
The present invention also includes the improvement to the apparatus shown in U.S. Pat. No. 5,626,192 of incorporating a selection of time delays in the electric means which prevents the solenoid valve from being actuated before it is desired. This reduces the power drain on the batteries as the tool is run into the well until the desired depth of the tool has been reached. The circuitry provides a fixed test period prior to activation of the time delay which allows the tool to be functionally checked before it is run into the well.